In general, the internal combustion engine (hereinafter simply referred to as “engine”) of this type has a crankcase in which is collected such a blow-by gas leaked from combustion chambers through clearances between cylinders and pistons during the compression and power strokes. The leaked blow-by gas contains unburned air-fuel mixture and burned exhaust gas as well as a lot of water with a strong acidity, thereby causing deteriorating the quality of engine oil and forming corrosion on elements or parts in the engine. To prevent the quality of the engine oil from being deteriorated and to avoid the elements or parts from being corroded, the engine is usually equipped with a positive crankcase ventilation (PCV) type of blow-bay gas returning apparatus to forcibly ventilate the crankcase for returning the blow-bay gas to each of the combustion chambers of the engine through the return pipe and the intake pipe.
More specifically, in the blow-bay gas returning apparatus, the blow-by gas collected in the crankcase is separated into gas and liquid by an oil separator, and then returned to the inside of the intake pipe through a PCV valve and a PCV hose, i.e., the return pipe for returning the blow-by gas to the engine. The PCV hose has one end portion connected to the intake pipe partly forming the intake pipe structure according to the present invention.
When the automotive vehicle equipped with the blow-bay gas returning apparatus is used in the cold regions, the inner surface of the intake pipe in the vicinity of the one end portion of the PCV hose, i.e., the return pipe is apt to have ice coated and accumulated thereon from water contained in the blow-by gas due to the temperature of the air flowing in the intake pipe dropped below zero degree especially at a time of an idling operation of the engine. When the ice is grown to an excessively large size, the intake pipe and/or the return pipe is frequently blocked by the ice, thereby making it impossible for the blow-by gas to be returned to the combustion chamber of the engine. In case of the large ice blocks being separated from the inner surfaces of the intake pipe and/or the return pipe, the ice blocks may lead to damaging impellers of a supercharger.
To overcome these problems, there have so far proposed a wide variety of intake pipe structures which are devised to avoid as much as possible such a situation in that water frozen becomes ice coated and grown on the inner surfaces of the intake pipe and/or the return pipe to block the intake pipe and/or the return pipe, thereby resulting in an ineffectiveness to the gas returning operation.
One of the conventional intake pipe structures is disclosed by Japanese Utility Model Application Publication No. 5-30411, and comprises a PCV hose having one end portion extending into and opened at the inside of an intake pipe and flared in the form of a trumpet shape to prevent the PCV hose from being blocked by ice blocks at the time of the accretion of ice on the inner surfaces of the intake pipe. Another conventional intake pipe structure is disclosed by Japanese Utility Model Application Publication No. 3-42011, and comprises a PCV hose having one end portion connected with an intake pipe and made of rubber. The PCV hose is attached to the intake pipe with its center axis inclined to the center axis of the intake pipe so that water is flown on and along the inclined inner surface of the hose into the intake pipe without being frozen.
A further conventional intake pipe structure is disclosed by Japanese Utility Model Application Publication No. 2-126012 as having a rubber tube coated on the inner surface of a PCV hose. The rubber tube has a high insulation property which renders it impossible for water to be frozen on the inner surface of the PCV hose. A still further conventional intake pipe structure is disclosed by Japanese Utility Model Application Publication No. 4-47116 to have a water reservoir provided below a gas returning opening to allow water to pass therethrough but to prevent ice rocks grown from frozen water from leaping out of the water reservoir. Also, Japanese Patent Application Publication Nos. 2000-145555, and 2005-120977 disclose a plurality of partition walls provided to form a snaked passage serving to separate blow-by gas into gas and liquid in the vicinity of a joint pipe unit connecting a breather passage with a return passage. Also, an apparatus is known by Japanese Patent Application Publication No. 2003-65171 to have annular protrusions and recesses surrounding a sensor and formed on a projection portion projecting from the inner surface of a surge tank to receive and stop water and oil.
However, the above conventional intake pipe structures of the internal combustion engine encounter such a problem that the blow-by gas return pipe is liable to produce ice therein by water contained in the blow-by gas in the vicinity of its joint portion with the intake pipe when the blow-by gas is mixed with cold fresh air introduced in the joint portion, thereby leading to blocking the return pipe and/or the intake pipe, and thus causing an ineffectiveness to the returning action of the blow-by gas. The ineffectiveness of the returning action of the blow-by gas results in raising an inner pressure in the crankcase, while the ice grown and separated from the inner surfaces of the intake pipe and/or the return pipe possibly gives rise to damages to the impellers of a turbocharger (turbo-supercharger).
If there are annular steps and other configurations of ledge formed on the intake pipe and/or the return pipe in the vicinity of the joint portion thereof, the flow of the blow-by gas is brought out of contact with, viz., separated from the inner surfaces of the intake pipe and/or the return pipe at around the steps and other configurations of ledge where there are formed flow cavities between the flow of the blow-by gas and the inner surfaces of the intake pipe and/or the return pipe. This means that the conventional intake pipe structures encounter such a problem that when the vehicle is used in the cold regions, the flow cavities facilitate forming and growing ice on the inner surfaces of the intake pipe and/or the return pipe near the annular steps or other forms of step since each of the flow cavities has a relatively low pressure. Further, the angle of the return pipe with respect to the intake pipe near the joint portion thereof, the shape of the inner surface of the return pipe near its joint portion with the intake pipe, and the length of a curved inner surface portion of the return pipe may greatly influence on the accretion of ice and the separation of ice blocks on intake pipe and/or the return pipe.